1. Field of the Invention
The present invention relates to a golf club by which the directional stability and flight distance of a shot ball can be improved.
2. Description of the Related Art
In a conventional wooden club, as well as to a metal wood club, a head is in such a shape that, as shown by two dashed line in FIG. 1, it gradually expands from a shaft side to a toe side. The center of gravity of the head is set at a position inclined toward the toe side rather than the center of the projection plane of the head, thereby the head speed of the golf club may be increased at the time of impacting on the ball.
Also in a conventional golf club of an iron type, according to the similar theory, an end of the back side of a club face part is, when seen from a plane, smoothly connected to the hosel, through a neck part, forming a curve (See dashed line A in FIG. 6) and thus the center of gravity of the club is set at a position slightly inclined toward a toe side.
However, when the center of gravity of the head inclines toward the toe side, as shown by two dashed line in FIG. 2, and when the head B is rotated with holding an end A of the club shaft, a radius R0 of the rotation, with its center line of the rotation positioned at the vertical line made by suspending an upper end of the shaft, increases. Therefore, the metal wood club and the iron club, as shown in FIGS. 3(a) and 11(a), respectively, are apt to cause covering motion (which means the phenomenon that the toe side goes fast than the shaft side as if the toe side rotates around the shaft side) at each head toe side just before impacting.
For the purpose of inhibiting a hook flying of the shot ball, caused by the covering motion, in the metal wood club, as shown by two dashed line in FIG. 1, a head face surface usually has such a shape that the shaft side expands slightly more forward than the toe side. Accordingly, curvature along the transverse direction of the face surface and curvature along longitudinal direction of the face surface are not the same; usually curvature along longitudinal direction is larger than that along the transverse direction.
On the other hand, as shown in FIG. 10, the covering motion is not the only problem in the iron club; that is, the center of gravity of the iron club slightly inclines toward the toe side in the club face part, therefore for advanced golfers whose down swings are faster than those of beginners, a toe down phenomenon, in which the neck part is twisted downwardly by an accelerated motion applied to the head and thus the toe side of the club face part tends to be lowered, resulting in a duff shot.